Casein kinase II is a cyclic-nucleotide independent Ser/Thr protein kinase which is highly conserved among eukaryotic organisms. The enzyme phosphorylates a wide spectrum of endogenous substrates, including translational initiation factors, membrane proteins, soluble enzymes, and a variety of nuclear proteins including the RNA polymerases. Although the physiological role of casein kinase II is not known, its broad substrate specificity suggests that the enzyme is multifunctional and that it may coordinate a variety of diverse processes, including transcription, translation, cell cycle progression, and cell-cell communication. The importance of Ser/Thr protein kinases in cell metabolism is indicated by the fact that at least two retroviral oncogenes (v-mil and v-raf) encode a SER/Thr protein kinase, as does at least one yeast cell division cycle mutant (cdc 28). A better understanding of casein kinase II should provide insight into both normal and abnormal cell behavior. The overall goal of the proposed research is to determine the physiological role of casein kinase II. The work makes use of Drosophila melanogaster as the experimental organism because of the potential for genetic analysis in this species. The specific aims of the research are: (1) to characterize in detail the structure and expression of previously cloned genes encoding the alpha and beta subunits of Drosophila casein kinase II, as well as a gene encoding a prominent endogenous substrate, chromosomal protein D1; (2) by a combination of classical genetics, P element- mediated transformation, and site-directed mutagenesis to generate null, conditional, and specifically engineered mutations in these genes for analysis of function in vivo; (3) to determine the functional consequences of casein kinase II-catalyzed phosphorylation of the beta subunit (autophosphorylation), protein D1, and topoisomerase II, another endogenous substrate of the enzyme; and (4) to evaluate the significance of a polymeric, filamentous form of the Drosophila kinase, in particular to determine whether filamentous casein kinase II exists in vivo, to determine whether polymerization regulates enzyme activity, and to identify activators and/or inhibitors which act by modulating protomer/polymer equilibrium.